Method of providing a hash value for a piece of data, electronic device and computer program

ABSTRACT

A hash value provides for a time-stamp for a piece of data upon verification. Providing the hash value includes deriving one-time signing keys of signer&#39;s one-time signing key hash chain by a one-way function of a secret key of the signer and a function of an index of the one-time signing key, and providing the hash value for the piece of data by a hash function including the piece of data and the derived one-time signing key. An electronic device having a processor arranged to implement a functional module for deriving a one-time signing key and providing a hash value for a piece of data by a hash function including the piece of data and the derived one-time signing key is also disclosed. The functional module is arranged to perform the method. A computer program for implementing the method on the electronic device is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. § 371of PCT/EP2016/050297, filed Jan. 8, 2016, which claims the benefit ofU.S. Provisional Application No. 62/118,808, filed Feb. 20, 2015, whichapplications are hereby incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present invention generally relates to a method of providing a hashvalue for a piece of data, where the hash value provides for atime-stamp for the piece of data upon verification. The method aims atproviding a one-time signing key in an efficient way.

BACKGROUND

“Big data”, cloud, and the Internet of Things (IoT) are examples of therapidly expanding area of distributed data networks and acquisition ofdistributed data. Data generated at a plurality of source nodes iscollected for processing and/or analysis. An example of the source nodesincludes sensor networks that perform measurements and providemeasurement data, e.g., in home automation data networks or industrialprocessing data networks. A further example includes servers in a datacenter generating event log records, e.g. for operational security.

The operation of data networks, such as above examples, relies upon theintegrity of the data received from the distributed data sources and thecontrol processes. This means that as data is collected, it has to bepossible to verify that the data has not been tampered with since thedata left the source node. Furthermore, the data source has to beauthentic. This means that an indicated source, e.g., a source nodeindicated by the received data or a data packet including the data, isthe actual originator of the data.

Depending on operational security requirements, it is not sufficientthat only the intended recipient collecting the data can verify aspectsof integrity and authenticity. Rather, it is required that third partiescan audit the data exchange between the source nodes and the collectingnode. Conventional techniques for authenticating the data sourceimplement public-key cryptography, e.g., using a Public KeyInfrastructure (PKI) with signatures on all data exchanged between thenodes.

However, generating signatures is resource consuming in minimalisticsource nodes (also referred to as “low-end devices”) such as sensors.Furthermore, the impact of signatures on bandwidth and/or storage isdisproportionally large compared to the data to be exchanged (e.g.,since the nodes have to be prepared for an audit, a large number ofsignatures have to be stored for relatively long time periods in thenodes). Moreover, signatures verifiable by a PKI are known to becumbersome to establish and maintain over time, especially if manysources of data have to be distinguished, i.e., identified by means ofdifferent certificates.

Other conventional techniques, e.g. below referred to as QI-KSI,implement Merkle trees. Aggregating hash values of the exchanged data ina Merkle tree is efficient, since the “root” of the Merkle tree providesa compressed digest of all individual hash values, so that the Merkletree reduces storage requirements. However considerable effort is neededto arrange for the keys in each leaf of the tree to be used forauthentication.

Ahto Buldas, Andres Kroonmaa and Risto Laanoja have disclosed someprinciples in “Keyless Signatures’ Infrastructure: How to Build GlobalDistributed Hash-Trees”, below referred to as [1], in “EfficientQuantum-Immune Keyless Signatures with Identity”, below referred to as[2], in “Efficient implementation of Keyless Signatures with HashSequence Authentication”, below referred to as [3], and in “SecurityProofs for the BLT Signature Scheme”, below referred to as [4]. AhtoBuldas and Sven Laur have disclosed some principles in“Knowledge-Binding Commitments with Applications in Time-Stamping”,below referred to as [5].

Every time the client wants to authenticate himself, a value z_(k) needsto be recomputed from z_(n), as will be further described in thisdisclosure. This may be a problem if n is large and there is no capacityto store or re-compute the whole hash chain. The solution to thisproblem is the technique called “hash sequence traversal”. One suchtechnique was proposed by D. Coppersmith and M. Jakobsson in their paper[6]. In order to derive z_(k) faster than just sequential hashing fromz_(n), to z_(k), the reversed order of hash chain z₀←z₁← . . . ←z_(k)← .. . can be derived in average log(n) time if one could keep log(n) ofintermediate hash values of the hash sequence.

A short description of the M. Jakobsson and D. Coppersmith technique onthe intuitive level can be given as follows. Assume the client can keepthe value z_(n/2), then the derivation of any value z_(k) would requireat most n/2 hashes, instead of n. Now let us assume that the clientkeeps two intermediate values z_(n/2) and z_(n/4). Thus, the elements ofthe first half of the hash chain z_(k), for k≤n/2, would requirere-computation of at most n/4 hashes. When k becomes larger than n/2,the intermediate value z_(n1/4) can be removed and a new value z_(n3/4)is derived linearly in time n¼ hash operations, so that the elements ofthe second half of the hash chain z_(k), for k>n/2, can be calculated inat most n/4 hashes as well. It has been shown that having log(n)intermediate hash values, the total time to derive the reverse-orderhash chain is log(n), in average.

Even if the approach described in [6] improves efficiency of generatingelements of the hash chain, it is a desire to provide furtherimprovements of the efficiency.

SUMMARY

The invention is based on the understanding that a one-time signing key,OTSK, may be generated by using a one-way function. The inventors havefound that a one-way function which operates on a secret key of thesigner and a function of an index of the OTSK hash chain provides thedesired OTSK.

According to a first aspect, there is provided a method of providing ahash value for a piece of data, where the hash value provides for atime-stamp for the piece of data upon verification. The method comprisesderiving one-time signing keys of signer's one-time signing key hashchain by a one-way function of a secret key of the signer and a functionof an index of the one-time signing key, and providing the hash valuefor the piece of data by a hash function including the piece of data andthe derived one-time signing key.

The function of the index may be the index itself.

The one-way function may be a cryptographic message authentication codefunction. Alternatively, the one-way function may be a hash function.

The method may comprise registering the provided hash value.

The method may comprise providing a one-time proof of knowledge of theone-time signing key to a signing authority entity without revealing theone-time signing key. The one-time proof of knowledge may include a hashpath for the hash value, and the providing of the one-time proof ofknowledge to the signing authority includes sending the index of theone-time signing key, the hash value and the hash path.

The method may comprise sending a signing request to a signing authorityfor a plurality of pieces of data, wherein each piece of data may beassigned a respective index consecutively by using one-time signing keyswith time-forwarded one-time signing key indexes.

The method may comprise applying a time fraction hash tree splitting atime slot corresponding to the index into time fractions such that thetime slot is divided into fractions according to the number of leafs ofthe time fraction hash tree.

According to a second aspect, there is provided an electronic devicecomprising a processor arranged to implement a functional module forderiving a one-time signing key and providing a hash value for a pieceof data by a hash function including the piece of data and the derivedone-time signing key. The functional module is arranged to perform themethod according to the first aspect.

The electronic device may be a wireless device.

The electronic device may be a network node.

According to a third aspect, there is provided a computer programcomprising instructions which, when executed on a processor of anelectronic device, causes the electronic device to perform the methodaccording to the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent invention, will be better understood through the followingillustrative and non-limiting detailed description of preferredembodiments of the present invention, with reference to the appendeddrawings.

FIG. 1 illustrates a hash tree structure.

FIG. 2 illustrates a Merkle tree and a corresponding ash path.

FIG. 3 schematically illustrates a KSI architecture.

FIG. 4 illustrates a simplified view of the KSI architecture.

FIG. 5 illustrates a model of signing documents in QI-KSI.

FIG. 6 illustrates a QI-KSI signing protocol.

FIG. 7 illustrates modified OTSKs in a QI-KSI solution.

FIG. 8 schematically illustrates an approach for deriving the OTSKsdirectly via a one-way function.

FIG. 9 illustrates a modified Trusted third party signing authority,TTP-SA, arranged to use a yet another Merkle sub-tree.

FIG. 10 illustrates an example when a time slot is split into fractions.

FIG. 11 illustrates an example of the approach of the fraction treecombined with an approach of delayed requests.

FIG. 12 is a flow chart illustrating a method according to anembodiment.

FIG. 13 schematically illustrates a wireless network with network nodesand a wireless device in which the invention may be implementedaccording to an embodiment.

FIG. 14 schematically illustrates a computer-readable medium and aprocessing device.

DETAILED DESCRIPTION

Certain embodiments disclosed herein relate generally to the technicalfield of security, and more particularly to the field of hash functions.For the easier understanding of the contribution by the invention, anintroduction to mechanisms for providing hash functions used for timestamping is demonstrated below. For further facilitating the reading ofthis disclosure, commonly used abbreviations are listed below.

ABBREVIATIONS

Abbreviation Explanation

-   -   BLT Extension of KSI    -   CRH Calendar root hash    -   GW Gateway    -   KSI Keyless Signature Infrastructure    -   HMAC specific message authentication code algorithm construction    -   MAC message authentication code algorithm (generic)    -   PKI Public Key Infrastructure    -   TSA Time-Stamp Authority    -   PKI Public Key infrastructure    -   QI-KSI Quantum-Immune KSI, e.g. BLT    -   RH Root hash of a Merkle type of tree    -   HP Hash path of a Merkle type of tree    -   LRS Left-Right Sequence of a hash path    -   AHP Aggregation hash path    -   ARH Aggregation root hash    -   CHP Calendar hash path    -   CRH Calendar root hash    -   TTP Trusted third party    -   TTP-SA Trusted third party signing authority    -   CA Certificate Authority    -   SK Secret key    -   PK Public key    -   HC Hash chain    -   OTSK One time signing key    -   OTAK One time authentication key        Introduction to KSI

KSI stands for the “Keyless Signature Infrastructure. This section isbased on open sources, such as publications of papers [1-5] mainly onthe cryptographic e-print web-based database where the authors describedifferent aspects of the KSI. The term “keyless signature” that is usedin references [1-5] could be seen as slightly misleading. Another term,in the field of cryptography, that could be used instead is a “timestamp” of a given hash value, from the client's perspective. Forconsistent terminology with earlier work, we will nevertheless stickwith the term KSI in the text below.

Merkle Trees and Hash Paths

FIG. 1 illustrates a Merkle hash tree where H is a pre-defined hashfunction. The KSI is based on the well-known Merkle hash treeconstruction, a hash tree structure. The hash tree or Merkle tree is atree in which every non-leaf node is labelled with the hash of thelabels of its children nodes. Hash trees are useful because they allowefficient and secure verification of the contents of large datastructures. Hash trees are a generalization of hash lists and hashchains. Demonstrating that a leaf node is a part of the given hash treerequires processing an amount of data proportional to the logarithm ofthe number of nodes of the tree; this contrasts with hash lists, wherethe amount is proportional to the number of nodes. FIG. 1 shows anexample of such a tree with 4 leafs. The tree's leafs are digests of apre-defined hash function H. The next layer includes two nodes with hashvalues h₀₁ and h₂₃ that are derived from the adjacent children leafs asthe hash of the concatenation of the leafs' digests. The root hash (RH)is computed as the hash of the concatenation h₀₁∥h₂₃ (the order of theconcatenation is important). This way, given the values on the tree'sleafs one may compute the root hash that actually binds all the valuesof leafs together. i.e., changing any value in any leaf implies a changeof the RH value.

Another notion that we will use is the Hash Path (HP), which is anordered sequence of hash values that helps to derive the root hash,starting from a chosen leaf value. FIG. 2 shows an example of a Merkletree with 8 leafs, as illustrated in FIG. 2a , and the correspondinghash path for the leaf h₃, as illustrated in FIG. 2b , that includes thesequence of “missing” nodes of the tree needed for the completederivation of the RH. Note that the “missing” hash values in each nodeare added to the child's hash value either from the left (L) or from theright (R) side. The ordered sequence of “L” and “R” marks of a given HPis a left-right sequence (LRS) of a given HP.

Thus, the path can be written as the sequence of 4 hash values{h₃;h₂(L);h₀₁(L);h₄₅₆₇(R)}, and having the sequence of “L-R” marks onecan compute the root hash explicitly.

It is also worth to note that an LRS is 1-to-1 mapped to the index ofthe leaf, if the LRS is translated into the binary representation withthe following rules: L-R marks closer to the root represent the mostsignificant bits of the index, and closer to the leafs represent theleast significant bits of the index; L is translated to the bit value 1and R is translated to the bit value 0.

Indeed, in the example illustrated in FIG. 2b of the hash path for h₃the L-R sequence is “RLL”, and it is translated to the correct index011₂=3.

As a final comment we note that we actually can change the hash functionas we move through the tree. In that case an identifier of the hashfunction used in each merging node has to be encoded into the path.

KSI Architecture

A basic drawing of the KSI architecture is shown in FIG. 3. That is,FIG. 3 illustrates KSI's global Merkle tree and its layers. KSI makes itpossible for many users to collectively insert their hash values intothe distributed Merkle tree and to compute the collective root hash, ata given time slot.

The KSI system architecture includes several layers of aggregators, thefunctionality of each is basically to accept multiple hash values fromthe children connections, produce the local root hash, and push it tothe upper layer for further aggregation. There are physically manyaggregators on each layer that are distributed world-wide, but in theFIG. 3 there is only one hash path is shown, from the below singleclient to the top RH.

A client or a device may push its own hash value using the entry pointcalled the Gateway. The Core Network (CN) is the last “station” ofaccumulating hash values into the large Merkle tree, and CN thuscomputes the aggregation root hash (ARH).

Additionally, CN has an extra modified Merkle tree to add the timestamping to ARE at a given time. The Calendar tree is organized such away that it includes both the current ARE and the history of allprevious ARHs in the past. The result of the Calendar tree is theCalendar Root Hash (CRH).

As the result of aggregation, the client receives back the aggregationhash path (AHP) from the client's hash value to the aggregation roothash, and also the calendar hash path (CUP) from the ARE to the globaltime stamp hash value that is actually the CRH.

The Core Network beats at regular intervals, for example, say once persecond, which means that the CRH and the calendar tree are updated everysecond. CN also keeps the history of the global time-stamps for eachsecond slot—the combination of ARHs and all historical CRHs in the past.

This way, the client or anyone else can later verify that thecombination of a saved aggregation hash path and the calendar hash pathat a certain time t lead to the correct value. I.e., LRS of AHP could beserved as a static identifier of the Gateway (if the connection of theGateway to the KSI infrastructure is static), and LRS of CHP is used toverify the time when the hash paths were created.

The global time stamp value CRH can be periodically published in anewspaper so that the Core Network cannot itself to modify the globaltime stamp back in time.

For verification purposes, the CRH can be received either off-line, oron-line. For off-line use cases one could take the CRH through theprinted publications (that may be periodically once per month). Foron-line verification use cases, the CM can be signed by a trusted entity(perhaps, including a certificate), and then it can be downloaded byclients and/or applications at any time for verification purposes.

In the general architecture of KSI the entry point for clients (and/orapplications) is the Gateway (GW) that itself can be an aggregationlayer, but additionally provides the client's front-end for variousservices based on KSI's time-stamping infrastructure. This way, theGateway can be seen as a server-based service engine that should belocated close to the customer, or actually be on the customer's side.

The list of possible services that the Gateway may assist with includes:time-stamping of a given hash value, assistance in signing a document,etc. All those services are not really a part of KSI, but some of themare a part of QI-KSI.

FIG. 4 illustrates a simplified view of KSI structure, and we may nowrefer to the simplified FIG. 4 of the KSI architecture.

Identifier vs Identity

KSI returns the aggregation hash path and the calendar hash path. TheAHP may be considered as the identifier of the Gateway, since the L-Rsequence in the global Merkle tree determines the way the Gateway wasconnected to the KSI. However, this identifier may be valid if certainconditions are valid:

-   -   (a) The logical connection of the Gateway to KSI's leaf is        static    -   (b) A certificate that binds the Gateway's identity with the        identifier is issued.

Later we will see how the identifier is used in the QI-KSI signingmodel.

Introduction to QI-KSI

QI-KSI stands for “Quantum-Immune KSI”. This section is mainly based onthe papers [2] and [4] identified in the introductory part of thisdisclosure.

QI-KSI is an extension for KSI and provides two hash-based techniques.Hash-based cryptography is, as of today, believed to be quantum immune,so this is the reason for the name “quantum-immune”. QI-KSI proposes thetechnique for a hash-based authentication, and a hash-based digitalsignature architecture with the help of KSI's time-stamping service.

Hash Chains for Authentication

This is based on one-time passwords techniques. The client (and/orapplication) selects a random secret value z_(n) (of size of the hashdigest), and generates the hash chain (HC) z₀←z₁← . . . ←z_(n) asfollows:

-   -   z_(i)=H(z_(i−1)), for i=0 . . . n−1, and H is a chosen hash        function.

The value z₀ is then shared with the server side (via some channel) towhich the client is intended to authenticate himself.

At any given time, the server holds a value z_(k) (in the beginning, theserver holds the value z₀). When the client wants to authenticatehimself, he uses and sends to the server the value z_(k+1). The serververifies that H(z_(k+1))=z_(k) and if the values coincide then theauthentication is successful. In the latter case, the server throws awayz_(k) and holds z_(k+1), instead, for future authentications.

This way, one secret key z_(n) can be served for n authentications.

Hash Sequence Traversal Technique

In this scheme, every time the client wants to authenticate himself, thevalue z_(k) needs to be recomputed from z_(n). This may be a problem ifn is large and there is no capacity to store or re-compute the wholehash chain. The solution to this problem is the technique called “hashsequence traversal”. Such a technique was proposed in [6] by D.Coppersmith and M. Jakobsson. In order to derive z_(k) faster than justsequential hashing from z_(n) to z_(k), the reversed order of hash chainz₀←z₁← . . . ←z_(k)← . . . can be derived in average log(n) time if onecould keep log(n) of intermediate hash values of the hash sequence. Ashort description of the M. Jakobsson and D. Coppersmith technique onthe intuitive level can be given as follows. Assume the client can keepthe value z_(n/2), then the derivation of any value z_(k) would requireat most n/2 hashes, instead of n. Now let us assume that the clientkeeps two intermediate values z_(n/2) and z_(n1/4). Thus, the elementsof the first half of the hash chain z_(k), for k≤n/2, would requirere-computation of at most n/4 hashes. When k becomes larger than n/2,the intermediate value z_(n/4) can be removed and a new value z_(n3/4)is derived linearly in time n¼ hash operations, so that the elements ofthe second half of the hash chain z_(k), for k>n/2, can be calculated inat most n/4 hashes as well. It has been shown that having log(n)intermediate hash values, the total time to derive the reverse-orderhash chain is log(n), in average.

QI-KSI Signing Model

The model of signing documents in QI-KSI is showed in FIG. 5. The client(or the Gateway, if the signing key is delegated), needs to create asecret signing key, and get a certificate from a CA on the public key.In this model, we look on the solution where a Trusted Third Party (TTP)behaves as a Signing Authority (TTP-SA) and takes part of the signingprocess and performs time-stamping of client's signing requests.

In QI-KSI, the signer first creates his own pair of the secret key andthe public key. The signer chooses a random secret key z_(n). Then, thesequence of values (hash chain) z₀← . . . ←z_(n) is computed as

-   -   z₁=H(z₁+1) for i=0 . . . n−1, and H is a chosen hash function.

The value z₀ is the public key and a relevant certificate for the publickey z₀ is generated by an external certificate authority (CA). The valuez₀ is bound with the user's identity in the validity time t₀ secondsfrom a well-known date (number of seconds from the date 1970-01-01 andtime 00:00:00) that determines the time after which the certificate isvalid. To be more precise, a certificate should include at least thefollowing fields: Cert:={Client's identity records; z₀, t₀, TTP-SA'sidentity and identifier}, where the TTP-SA's identifier can be the indexof the leaf in the global KSI Merkle tree to which the TTP-SA isstatically attached.

QI-KSI signing key looks similar to the hash chain in the QI-KSIauthentication method, but the difference comes from the meaning of theindex k in the notation z_(k). The values z_(k), k=1 . . . n, are usedas one-time signing keys (OTSK) each of which can be used only at acertain KSI's time frame that is exactly (t₀+k)th second from the globalstarting time (recall, the Core Network “beats” and produces global timestamp values with the speed once per second).

QI-KSI Signing Protocol

QI-KSI signing protocol, see e.g. paper [2], is shown in FIG. 6. If theclient wants to sign a piece of data, e.g. some message M, at a certaintime slot t>t₀, such that t=t₀+i, then he takes the OTSK z_(i) andcomputes x=H(H(M);z_(i)) The value of x together with the user's ID issent to the TTP-SA. TTP-SA checks that the client's certificate has notbeen revoked. Then TTP-SA pushes the hash of x∥ID to KSI in order to getthe time stamping. The returned blob S_(i) contains the identifier ofTTP-SA, that is its static LRS of AHP, the hash path and the calendarpath. CA sends S_(i) back to the user. After the time-stamp is returned,and the current time t becomes larger than t₀+i seconds, the OTSK z_(i)can be revealed. The signer then publishes the signature as <ID, i,z_(i), S_(i)>.

The verifier may check that z_(i) is actually the i:th pre-image of z₀,and the time stamp corresponds to t₀+i.

QI-KSI Improved OTSKs for Verification

FIG. 7 illustrates modified OTSKs in a QI-KSI solution. In the QI-KSIsigning protocol, the signer may derive the OTSK z_(i) in log(n) timewith the help of log(n) intermediate hash values using the hash sequencereversal technique, as it was described earlier.

The problem comes for the verifier who wants to check the signature, ashe only knows z_(i) but needs to verify it against the public key z₀.The verifier does not have those intermediate hash values and thus hasto perform i hashes starting from z_(i) and going all the way to z₀.

In order to reduce the time and/or complexity of the verificationprocess, the following modification to OTSKs was proposed. This includesbuilding yet another modified Merkle tree on top of OTSKs as shown inFIG. 7.

The client's certificate additionally includes the root hash r, and thesignature additionally includes the hash path from the OTSK z_(i) to theroot r. Thus, the verifier only needs to check that z_(i) participatedin the hash root generation, and the L-R sequence of the hash path istranslated to the correct index i.

For efficiency reasons, the signer needs to keep the relevant part ofthe hash-tree, and in the signing process the part of the hash tree thatleads to the root hash r may be partly recomputed in log(n) time withlog(n) intermediate hash values. That computation also requires theknowledge of other values z_(i) in an efficient way, but then this partmay be done with a hash chain traversal technique as demonstrated inU.S. provisional patent application No. 62/118,808.

Synchronization with KSI

It is important that S_(i) returned by TTP-SA corresponds to the OTSKz_(i) that has been used by the client. QI-KSI proposes the idea thatthe client actually needs to use 3 (or more) keys z_(i), z_(i+1) andz_(i−2) and send a parallel request to TTP-SA for time-stamping. Thesigner will get 3 time stamps S's, but the stamp's time will correspondto only one of z_(i) . . . z_(i+2).

All this also means that the signer can produce one signature per 3 timeslots, i.e., one signature per 3 seconds. However, as will bedemonstrated below under the headline ‘Further Options’, efficiency maybe improved also in this sense.

The gist of this disclosure will now be presented, followed by someoptional features, and thereafter further disclosure about methods andtheir implementations. It is readily understood from this disclosurethat any combination with the demonstrated features of the KSI conceptare applicable.

Deriving the OTSKs Directly Via a One-Way Function

FIG. 8 schematically illustrates an approach for deriving the OTSKsdirectly via a one-way function. It may be a desire to improve the partof deriving the one time signing keys, OTSK's, values z_(i) of thesigner's OTSK hash chain. The derivation of z_(i):s traditionallyrequires, even with the M. Jakobsson and D. Coppersmith technique of[6], the signer to spend additionally log(n) time for each z_(i), and tostore additionally log(n) intermediate hash values. However, asdescribed below, this can be done in O(1) time without storingintermediate hash values.

We propose that instead of the hash chain z₀← . . . ←z_(n), as discussedabove, where z_(n) is the secret key and z₀ is the public key, thesigner derives any of the OTSKs directly via a one-way function, giventhat all z_(i)s are bound by the root of a Merkle tree on top of theOTSKs sequence {z_(i)}.

Instead of the hash chain z₀← . . . ←z_(n), the signer may derive any ofthe OTSKs as follows:

z_(i)=H(z_(sk);f_(i)), for i=1 . . . n, where H is a one-way function,where z_(sk) is a secret key of the signer, and f_(i) is a function onthe index i that generates different values for each i=1 . . . n. Forexample, this function can be as simple as fi=i, but it may be a morecomplex one. As an alternative, the z_(i):s may be generated asz_(i)=HMAC(z_(sk);f_(i)). The new scheme is shown in FIG. 8, where theupper part, i.e. above the dotted line, shows the verification of theOTSK values which is performed in the same way as demonstrated above,e.g. with reference to FIG. 7. The difference in this approach is thusthe way the OTSK values are derived, i.e. by the one-way function.

The signer's certificate then does not need to have z₀, but it maycomprise: the user's identity records, the root hash value r thatcombines all OTSKs, the value n that indicates the expiration time forthe secret key z_(sk) as well as determines the height of the tree, andthe validation time t₀, after which the certificate is valid. Since theLRS of the hash path encodes the index of z_(i) uniquely, then this isthe way to verify that z_(i) is actually the OTSK that corresponds tothe time t₀+i

The root hash thus still can prove that the hash path of OTSK z_(i) wasoriginated from the same secret source. The LRS of the hash path fromz_(i) to r determines the time slot when the OTSK z_(i) can be used andbe verified against the returned time-stamp.

The use of z_(sk) makes it faster and/or requires less processing/memoryresources for the signer to derive the values z_(i) for any i at anytime without having to keep O(log(n)) intermediate hash values and spendO(log(n)) of time to derive z_(i), or calculate all hash values in thehash chain from z₀, z_(n−1), . . . , etc.

Since in this modification the certificate now includes the expirationtime (that is equal to t₀+n), and the TTP-SA also checks for thevalidity of the signer's certificate, then this scheme will be as secureas the one proposed in QI-KSI above, and it is more efficient.

After the expiration of the key usage time, the secret key z_(sk) can bethrown away, whereas all created signatures remain valid in time andverifiable.

By this, the signing process is faster and/or requires less storageresources (Cf. M. Jakobsson and D. Coppersmith technique) for theintermediate state, or requires less processing resources (Cf.traditional approach without M. Jacobsson and D. Coppersmith technique).

The above mentioned approach is also applicable for deriving other OTSKvalues, as will be described below.

Thus, for the QI-KSI signal model, there is provided a method to processfor a hash tree infrastructure at predetermined intervals presentedderived values of data to obtain a root hash value referred to astime-stamps that may be published such that the presented hash values tobe processed depend on previously published root hash values, and aprocesses to compute and deliver a signature for the data after checkingby a trusted signing authority wherein the derived values are the hashor mac of the data using an one-time signing key that is computed by amessage authentication function. As demonstrated above, the one-timesigning key may be computed as z_(i)=H(z_(sk);f_(i)), for i=1 . . . n,where H is a one-way function, where z_(sk) is a secret key of thesigner, and f_(i) is a function on the index i that generates differentvalues for each i=1 . . . n. The function may be f_(i)=i.

Further Options

The approach of deriving the OTSKs directly by a one-way function hasbeen shown above to provide an efficient way to provide the OTSK andthus hash value for a piece of data for use in the KSI context aspreviously known. Below, the applicability for further developments ofthe KSI approach and novel features thereof will be demonstrated.

One-Time Proof of Knowledge for One-Time Signing Keys in Hash BasedSigning Schemes

FIG. 6 shows how the signing protocol uses TTP-SA. The TTP-SA issues atime stamp of the signing request only when the client's certificate isvalid. This builds the trust for the verifier that at the time when thesignature was actually created, the client's certificate has not beenrevoked. Therefore, the verifier does not need to check the status ofthe client's certificate during the verification time.

A problem may be that TTP-SA does not know the content of the valuex—one part of the signing request, in the way that x (the value that theclient derives and sends to TTP-SA; see section “QI-KSI SigningProtocol” above) can be anything and be generated by anyone.

While issuing a signature, TTP-SA also does not know if the signingrequest comes from a legitimate user or from someone else. Hence, theTTP-SA may start to work and later when almost everything is ready findout that the user was not legitimate.

It may thus be desirable to have a solution where the TTP-SA couldverify that it is the authorized client who sends the signing request onhis name, which would build a better trust in the signature.

By using the hash path of a hash image of the actual OTSK as the proofthat the user actually knows the not yet public secret OTSK, the TTP-SAmay be better protected from doing work for non-legitimate requestors.The signer's signature may be shorter, and verification faster. The usersends this proof to the TTP-SA along with the signing request, so thatthe signing authority can verify the legitimacy of the signer beforeactually producing a signature fingerprint.

The way to generate OTSKs by a user and the usage of such aproof-of-knowledge is not limited by the described use case, and theapproach demonstrated here may be combined with any of the otherapproaches demonstrated in this disclosure. However, the benefit ofderiving the OTSK by a one-way function as demonstrated above is evidentwhen used together with this approach of providing one-time proof ofknowledge to a signing authority.

FIG. 7 illustrates how the hash chain is built (and FIG. 8 illustratesan alternative approach thereof) and its elements are used as OTSKs. Forefficiency reasons on the verifier side, the combined root hash r of allOTSKs in the modified Merkle tree is public and included in the signer'scertificate.

By including the path from z_(i) to the root r in the signature, theverifier is enabled to

(a) check in O(log(n)) time that z_(i) has been participated in thecomputation of the root value r and, by this way, to prove that z_(i) isvalid; and

(b) the LRS of the hash path from z_(i) to the root hash r also encodesthe index i of the OTSK z_(i) and, thus, the verifier can compare thetime t₀+i against the KSI's time-stamp's time slot, and that z_(i) wasused in the correct time slot.

The hash path from r_(i)'s (where r_(i)=H(z_(i))) to the public roothash r is actually the one-time proof of knowledge (OTPoK) of the secretOTSK z_(i), without revealing zi.

By the client sending the OTPoK of the secret key to the TTP-SA alongwith the request, the TTP-SA may (additionally) verify that the OTPoKcorresponds to the client's public key r that is stored in the client'scertificate. The TTP-SA may add the value of r_(i) into thetime-stamping process.

Thus, in the pair z_(i)→r_(i) the value r_(i) “authenticates” to theTTP-SA the value of the OTSK z_(i).

As a positive side effect, the signer's signature does not need toinclude the hash path from z₁←r, but only the OTSK z_(i), if TTP-SAincludes r_(i) as the part of the time-stamping computation. Theverifier sort of “exports” the need to check of the hash path z_(i)→r byletting the TTP-SA verify the hash path r_(i)→r before issuing thetime-stamp S_(i). The connection between z_(i) and r_(i) (and, thus, tor_(i)→r) can be verified later on if the TTP-SA pushes the hash of themodified vector {x; usedID; r_(i)} into KSI for time-stamping.

After a key generation, the signer has the sequence of OTSKs {z₁ . . .z_(n)}, that are valid for signing at times t₀+i time slot of KSI. Theroot hash r of a Merkle tree with the leafs values r_(i)s, i=1 . . . n,where r_(i)=H(z_(i)) for some one-way function H, as demonstrated above.The client's certificate may include the vector: {user ID; r; t₀;TTP-SA's KSI identifier}

Signing of a message M at some time t=t₀+i, where t₀<t≤t₀+n, may thencomprise the following protocol:

1. Signer computes x=H(H(M); z_(i)) and sends to TTP-SA the vector {i;x; userID, HP r_(i)→r}, where HP indicates hash path.

2. TTP-SA picks the right certificate that matches the pair {userID; r}and checks that it has not been revoked.

3. TTP-SA checks that HP r_(i)→r is correct, and that LRS of that HP ismapping to the index i.

4. TTP-SA sends the hash of {x; userID; r_(i)} to KSI in time t=t₀+i,and receives the tune-stamping S_(i), that is AHP (aggregate HP) and CHP(calendar HP).

5. TTP-SA sends S_(i) back to the signer.

6. The signer reveals the signature of the message M as<userID;i;z_(i);S_(i)>

The verification process is considered successful if:

1. H(x=H(H(M);z_(i)), userID; r_(i)=H(z_(i))) is the leaf of S_(i);

2. LRS of S_(i)'s AHP leads to the correct TTP-SA's KSI identifier thatis bound in the signer's certificate;

3. S_(i)'s AHP and CHP lead to the correct CRH for the time t₀+i.

Thus, the approach may include that the signing authority receives aproof-of-possession before starting to process the request in the hashtree, computation and issuing of signature. The proof of possession maycomprise sending the OTPoK of the secret key to the TTP-SA along withthe request. The TTP-SA may verify that OTPoK corresponds to theclient's public key that is stored in the client's certificate. TheTTP-SA may add the value of r_(i) into the time-stamping process.

A device, application or session of a client may thus be arranged totransmit a proof-of-possession to a signing authority TTP-SA before theTTP-SA starts to process a request in the hash tree, compute and issueof signature. The transmission of the proof of possession may comprisesending the OTPoK of the secret key to the TTP-SA along with therequest.

A server operating a signing authority function may be arranged toreceive a proof-of-possession from a client, to verify whether the OTPoKcorresponds to the client's public key that is stored in the client'scertificate, and omit computation and issuing of a signature when theOTPoK does not correspond to the client's public key and compute andissue signature when the OTPoK corresponds to the client's public key.The TTP-SA may add the value of r_(i) into the time-stamping process.

Sending Sequence of Signing Requests to TTP-SA Using OTSKs WithTime-forwarded OTSKs Indexes

This part of the disclosure relates to Time Fraction Sub-Trees in HashBased Time Stamping Services for Faster Streaming of Requests ofServices. Consider that KSI RH (root hash) is computed for eachinterval. Further, assume the intervals to be 1 second (but of courseother interval settings are possible).

An issue may be how QI-KSI, as demonstrated above, proposes tosynchronize the OTSK z_(i) with the KSI's tune. In the QI-KSI solutiondemonstrated above, when the signer sends a signing request to theTTP-SA, the client may take a group of OTSKs, for example threeconsecutive signing keys z_(i), z_(i+1) and z_(i+2), and send 3 signingrequests to the TTP-SA simultaneously. The TTP-SA then can choose oneout of the given three whose i corresponds to the current KSI's time,and push it to the KSI for time-stamping in the proper time slot. Sincethe client may reveal OTSK z_(i+2) only at time t>t₀+i+2, this meansthat the client can produce a stream of signatures with the speed of 1signature per 3 KSI's time slots (that is 1 signature per 3 seconds,with the above discussed design of the KSI's Core Network).

For the use case where the client needs to sign a stream of datamessages, the QI-KSI's way to synchronize the time between the signerand KSI is not optimal. It is a desire to provide a bettersynchronization solution so that the client does not waste OTSK keys andcan perform signatures for a stream of data, e.g. with the speed inaverage of 1 signing per KSI's time slot (a second).

Consider that the signer is enabled to send the sequence of signingrequests to the TTP-SA using OTSKs with time-forwarded OTSKs indexes,and by this the client proposes the delay time before the actualtime-stamping procedure, so that there is enough time for TTP-SA toreceive the requests, prepare them and synchronize the time with KSI. Inthe use case where one needs to produce a stream of signatures, thissynchronization scheme, as will be demonstrated in further detail below,utilizes the KSI resources (in particular, KSI's time slots)efficiently, which makes the signing speed to converge to 1 signatureper one KSI time slot, in average.

Assume that the possible resynchronization time between the signer's andKSI's clocks can be at most Δ seconds (for instance, let Δ be 5seconds), including possible delays in communication between the signerand the TTP-SA. When the signer sends a signing request at his localtime t_(sig), he actually may use the time-forwarded OTSK with the indext_(sig)−t₀₊Δ, prepare and send a signing request to the TTP-SA.

The TTP-SA may have a local queue with incoming signing requests thatare already checked for the client's certificate and are waiting forbeing entered to KSI at the right tune for time-stamping. When the KSItime becomes aligned with the time of the first request in the queue,i.e., when the KSI's time becomes t_(sig)+Δ−1, the TTP-SA pushes thecorresponding hash value to the KSI infrastructure and receives theright time stamping.

Thus, the client reveals the stream of signatures with the delay of Δseconds. In the use case of a stream of signatures, the performance maythen converge to the speed 1 signature per KSI time slot.

Note that in the above the clocking is described as being 1 second.However it is readily understood that it is equally applicable to otherclocking interval settings.

A trusted signing authority applying a hash tree signing system may havea local queue that comprises signing requests that use a time-forwardOTSK that are already verified and which start further processing whenthe time with the hash tree system gets aligned. The OTSK may bedetermined by having the index t_(sig)−t₀+Δ.

The sending of the sequence of signing requests to TTP-SA using OTSKswith time-forwarded OTSKs indexes benefits from being combined with theapproach for deriving the OTSKs directly via a one-way function, and mayalso benefit from the approach for one-time proof of knowledge forone-time signing keys in hash based signing schemes, as well as with anapproach comprising a combination of them.

A device, application or session of a client may thus be arranged totransmit signing requests to a signing authority with time-forwardedOTSKs indexes.

A server operating a signing authority function may be arranged toreceive signing requests with time-forwarded OTSKs indexes, store themin a queue, and when the KSI time becomes aligned with the time of arequest in the queue to push the corresponding hash value to a KSIinfrastructure and receive the right time stamping Any calculations maybe pre-calculated for the requests of the queue.

Time Fraction Sub-Trees in Hash Based Time Stamping Service, or a FasterStreaming of Requests of Services

Consider that KSI RH (root hash) is computed for each interval. Further,assume the intervals to be 1 second (but of course other intervalsettings are possible). As it was also mentioned in the sectiondiscussing synchronization with KSI above, the synchronization that isproposed in QI-KSI makes it possible to the client to make 1 signing per3 seconds (3 KSI's time slots). However, in a use case when the clientneeds to sign a stream of data, this might be a performance bottleneck.

The solution demonstrated above has mainly been discussed in view of ageneral case where an external service (KSI's time stamping, TTP SAservice, other external modules that can, but not necessarily, behash-based) is available once per a time slot (like in KSI, the serviceis available once per second). However, in the solution demonstratedbelow, the technique is demonstrated based on the example of the QI-KSIsigning scheme for the sake of easier understanding for the reader.

By extending the global KSI tree with a time fraction Merkle sub-tree onthe TTP-SA node it is possible for one or more clients/gateways toperform signing for a stream of data items with the average speed fasterthan the speed of producing time stamps with KSI, i.e. faster thandemonstrated with reference to the disclosure of sending sequence ofsigning requests to TTP-SA using OTSKs with time-forwarded OTSKs indexesabove. It is to be noted that the approach demonstrated below may becombined with time-forwarded OTSKs indexes as demonstrated above forefficient provision of OTSK keys, e.g. for performing signatures for astream of data.

The approach makes it possible for the client to have only one hashchain of OTSKs, where each one-tune signing key corresponds to its ownfraction of a second. That sub-tree will serve as a KSI's time slotsplitter of a time slot into smaller time fractions.

FIG. 9 illustrates a modified TTP-SA. We propose that the TTP-SA isarranged to use a yet another Merkle sub-tree with K leafs. The purposeis to split the KSI's 1 second time slot into K fractions of the second.Each leaf of the sub-tree corresponds to the certain fraction of thesecond, and thus the TTP-SA may accept multiple signing requests fromone or multiple clients/gateways simultaneously, providing time-stampswith a better time-granularity than just 1 second.

OTSKs of clients thus may be modified in such a way that now the clientmay create K sets of OTSKs. One set corresponds to and is used withinone certain fraction of a second. FIG. 10 illustrates an example when atime slot is split into K fractions, where K=4 in the example.

For example, if the TTP-SA's time-splitting sub-tree has 4 leafs, thenTTP-SA is capable to perform 4 signatures per second, instead of 1 as ofthe original QI-KSI. The client generates 4 hash chains from 4 secretkeys z_(n) ⁽⁰⁾ . . . z_(n) ⁽³⁾ and uses the OTSKs produced by z_(n)^((k)) in the signing times t=t₀+i+k/4 seconds, for i=1 . . . n, k=0 . .. 3 (for the example of K=4; K may be selected arbitrarily to achievedesired granularity).

For each fraction of a second the TTP-SA returns, as the result ofsigning request, the same S_(i), but adds the hash path of the TTP-SA'stime fraction sub-tree that is also included by the signer into thefinal signature.

The verifier may apply:

-   -   the LRS of AHP as the identifier for TTP-SA;    -   the LRS of CHP to identify the time in seconds when the        time-stamp was created;    -   the LRS of the HP of the TTP-SA's time fraction sub-tree to        identify the fraction of the second when the time stamp was        created.

Note that AHP and CHP parts of S_(i) will be the same for all K signingrequests within the same time slot. However, the HP of the time fractiontree will be different. Also note that since TTP-SA enters K hash valuesto the leafs of the time-fraction tree's HP, the signer or anyone elsecannot ignore that HP since then the signature becomes invalid andnon-verifiable.

For synchronization purposes, the signer may still use the idea from theQI-KSI design demonstrated above, where for every fraction slot k=0 . .. K−1, the signer uses 3 consecutive OTSKs z_(i) ^((k)), z_(i+1) ^((k)),z_(i+2) ^((k)). In this case, the average signing speed is 1 signatureper 3/K seconds.

A device, application or session of a client may thus be arranged tosign for a stream of data items by a time fraction tree splitting a timeslot of a time stamping infrastructure into time fractions.

A server operating a signing authority function may be arranged toreceive multiple signing requests of a time slot of a time stampinginfrastructure by a time fraction tree splitting the time slot of thetime stamping infrastructure into time fractions.

As indicated above, the approach of the fraction tree may be combinedwith the approach of delayed requests. FIG. 11 illustrates an examplethereof. Assume that the TTP-SA has a time fraction sub-tree forsplitting 1 second into K fractions. The signer may create only one OTSKhash chain, but now z_(k) corresponds to the time (t₀+└k/K┘)^(th) secondand (k modulo K)^(th) fraction of the second. The client sends a streamof signing requests using the time “current time of the signer” and thedelay, t_(sig)+Δ, where Δ is the maximum resynchronization time (forexample, Δ may be 3.25 seconds) between the client's and the KSI'sclocks, including possible delays in communication and the processingtime of the TTP-SA. i.e., the client sends the requests using z_(k)s fornot the current time, but for the current time plus some time offset Δ.

The TTP-SA server collects signing requests, verifies the client'scertificate, and al locates the prepared hashes for the delayedcollective time-stamping (with KSI) into a sorted (by time) queue.TTP-SA will push the top of the time fraction sub-tree to KSIinfrastructure for time-stamping at a proper time. The hash root of thefraction tree can also be prepared by TTP-SA during the given delay Δ.Thus, the queue of TTP-SA may be just a queue of hash values waiting fortheir turns to be time stamped.

This way, TTP-SA has some time delay during which it can check therequest itself (and the certificate), prepare the time fraction subtree, calculate the root hash of that sub tree, and wait for the correctKSI's time to occur, in order to push the pre-computed hash into KSI fortime stamping.

Another solution could be that the possibility for a signer to add asigning request at a fraction of a KSI's time slot t closes shortlybefore the time t, such that TTP-SA would still have enough time toprepare the root hash of the time fraction tree before its root hash isto be pushed for KSI time-stamping at time t.

The server returns S_(i)s together with the hash paths of its ownsub-tree when the signing job for the group of requests is done, andcontinues to proceed with the next group of signing requests, taken fromthe local queue, checked and prepared in advance for the next second ofthe KSI's time slot.

Thus, the client can publish the received stream of signatures with thetime delay Δ, and the average speed 1 signature per 1/K second utilizingOTSKs efficiently.

A time stamp service provider applying a hash tree signing system of ahash-tree time-stamping part and a trusted signing authority (TTP-SA)may operate on given intervals for the TTP-SA, and there may be provideda time fraction sub-tree for splitting each interval into K fractions.The signer may create only one OTSK hash chain, where z_(k) correspondsto the time (t₀+(k div K))^(th) time interval, e.g. second, and (k modK)^(th) fraction of the interval.

A device, application or session of a client may thus be arranged tosign for a stream of data items by a time fraction tree splitting a timeslot of a time stamping infrastructure into time fractions, and bearranged to transmit signing requests to a signing authority withtime-forwarded OTSKs indexes.

A server operating a signing authority function may be arranged toreceive multiple signing requests of a time slot of a time stampinginfrastructure by a time fraction tree splitting the time slot of thetime stamping infrastructure into time fractions, wherein the signingrequests comprises time-forwarded OTSKs indexes, and the server isarranged to store them in a queue, and when the KSI time becomes alignedwith the time of a request in the queue to push the corresponding hashvalue to a KSI infrastructure and receive the right time stamping. Anycalculations may be pre-calculated for the requests of the queue.

A server operating a signing authority function may be arranged toreceive signing requests to a signing authority with time-forwardedOTSKs indexes, store them in a queue, and when the KSI time becomesaligned with the time of a request in the queue to push thecorresponding hash value to a KSI infrastructure and receive the righttime stamping. Any calculations may be pre-calculated for the requestsof the queue.

The generation of further OTSKs, as of the optional approachdemonstrated above, further emphasizes the benefits of deriving OTSKsdirectly by the one-way function.

Methods and Implementations

FIG. 12 is a flow chart illustrating methods according to embodiments.Variants, details and explanations have already been provided above, andthe flow chart should be considered as a rough, schematic and simplifiedillustration of the approach and some of its options.

One or more OTSKs are derived 100 by a one-way function. The respectiveOTSK is used to provide 102 a hash value using a hash function includingthe OTSK and a piece of data which is intended for time signing. One ormore of the following options may be included in the method: registeringthe hash value such that the piece of data at least later on may beverified regarding its presence at a time corresponding to an index ofthe OTSK used for providing the hash value; providing a one-time proofof knowledge, OTPoK, to a signing authority that the OTSK was inpossession of the signer at a certain time without revealing the OTSK;and sending a signing request to the signing authority using OTSKs withtime-forwarded OTSK indexes such that signing of the hashes of thepieces of data may be queued at the signing authority and the slotscorresponding to OTSK indexes can be efficiently used. Further optionsand variants have been demonstrated above.

A device, application or session of a client may thus be arranged toderive a one-time signing key z_(i) as z_(i)=H(z_(sk);f_(i)), for i=1 .. . n, where H is a one-way function, where z_(sk) is a secret key ofthe signer, and f_(i) is a function on the index i that generatesdifferent values for each i=1 . . . n. The function may be f_(i)=i.

FIG. 13 illustrates a wireless network comprising a more detailed viewof network node 200 and wireless device (WD) 210, in accordance with aparticular embodiment. For simplicity, FIG. 13 only depicts network 220,network nodes 200 and 200 a, and WD 210. Network node 200 comprisesprocessor 202, storage 203, interface 201, and antenna 201 a. Similarly,WD 210 comprises processor 212, storage 213, interface 211 and antenna211 a. These components may work together in order to provide networknode and/or wireless device functionality, such as providing wirelessconnections in a wireless network and allowing for a change in estimatedDL CC. In different embodiments, the wireless network may comprise anynumber of wired or wireless networks, network nodes, base stations,controllers, wireless devices, relay stations, and/or any othercomponents that may facilitate or participate in the communication ofdata and/or signals whether via wired or wireless connections.

Network 220 may comprise one or more of IP networks, public switchedtelephone networks (PSTNs), packet data networks, optical networks, widearea networks (WANs), local area networks (LANs), wireless local areanetworks (WLANs), wired networks, wireless networks, metropolitan areanetworks, and other networks to enable communication between devices.

Network node 200 comprises processor 202, storage 203, interface 201,and antenna 201 a. These components are depicted as single boxes locatedwithin a single larger box. In practice however, a network node maycomprises multiple different physical components that make up a singleillustrated component (e.g., interface 201 may comprise terminals forcoupling wires for a wired connection and a radio transceiver for awireless connection). Similarly, network node 200 may be composed ofmultiple physically separate components (e.g., a NodeB component and aRNC component, a BTS component and a BSC component, etc.), which mayeach have their own respective processor, storage, and interfacecomponents. In certain scenarios in which network node 200 comprisesmultiple separate components (e.g., BTS and BSC components), one or moreof the separate components may be shared among several network nodes.For example, a single RNC may control multiple NodeB's. In such ascenario, each unique NodeB and BSC pair, may be a separate networknode. In some embodiments, network node 200 may be configured to supportmultiple radio access technologies (RATs). In such embodiments, somecomponents may be duplicated (e.g., separate storage 203 for thedifferent RATs) and some components may be reused (e.g., the sameantenna 201 a may be shared by the RATs).

Processor 202 may be a combination of one or more of a microprocessor,controller, microcontroller, central processing unit, digital signalprocessor, application specific integrated circuit, field programmablegate array, or any other suitable computing device, resource, orcombination of hardware, software and/or encoded logic operable toprovide, either alone or in conjunction with other network node 200components, such as storage 203, network node 200 functionality. Forexample, processor 202 may execute instructions stored in storage 203.Such functionality may include providing various wireless featuresdiscussed herein to a wireless devices, such as WD 210, including any ofthe features or benefits disclosed herein.

Storage 203 may comprise any form of volatile or non-volatile computerreadable memory including, without limitation, persistent storage, solidstate memory, remotely mounted memory, magnetic media, optical media,random access memory (RAM), read-only memory (ROM), removable media, orany other suitable local or remote memory component. Storage 203 maystore any suitable instructions, data or information, including softwareand encoded logic, utilized by network node 200. Storage 203 may be usedto store any calculations made by processor 202 and/or any data receivedvia interface 201.

Network node 200 also comprises interface 201 which may be used in thewired or wireless communication of signalling and/or data betweennetwork node 200, network 220, and/or WD 210. For example, interface 201may perform any formatting, coding, or translating that may be needed toallow network node 200 to send and receive data from network 220 over awired connection. Interface 201 may also include a radio transmitterand/or receiver that may be coupled to or a part of antenna 201 a. Theradio may receive digital data that is to be sent out to other networknodes or WDs via a wireless connection. The radio may convert thedigital data into a radio signal having the appropriate channel andbandwidth parameters. The radio signal may then be transmitted viaantenna 201 a to the appropriate recipient (e.g., WD 210).

Antenna 201 a may be any type of antenna capable of transmitting andreceiving data and/or signals wirelessly. In some embodiments, antenna201 a may comprise one or more omni-directional, sector or panelantennas operable to transmit/receive radio signals between, forexample, 2 GHz and 66 GHz. An omni-directional antenna may be used totransmit/receive radio signals in any direction, a sector antenna may beused to transmit/receive radio signals from devices within a particulararea, and a panel antenna may be a line of sight antenna used totransmit/receive radio signals in a relatively straight line.

WD 210 may be any type of wireless endpoint, mobile station, mobilephone, wireless local loop phone, smartphone, user equipment, desktopcomputer, PDA, cell phone, tablet, laptop, VoIP phone or handset, whichis able to wirelessly send and receive data and/or signals to and from anetwork node, such as network node 200 and/or other WDs. WD 210comprises processor 212, storage 213, interface 211, and antenna 211 a.Like network node 200, the components of WD 210 are depicted as singleboxes located within a single larger box, however in practice a wirelessdevice may comprises multiple different physical components that make upa single illustrated component (e.g., storage 213 may comprise multiplediscrete microchips, each microchip representing a portion of the totalstorage capacity).

Processor 212 may be a combination of one or more of a microprocessor,controller, microcontroller, central processing unit, digital signalprocessor, application specific integrated circuit, field programmablegate array, or any other suitable computing device, resource, orcombination of hardware, software and/or encoded logic operable toprovide, either alone or in combination with other WD 210 components,such as storage 213, WD 210 functionality. Such functionality mayinclude providing various wireless features discussed herein, includingany of the features or benefits disclosed herein.

Storage 213 may be any form of volatile or non-volatile memoryincluding, without limitation, persistent storage, solid state memory,remotely mounted memory, magnetic media, optical media, random accessmemory (RAM), read-only memory (ROM), removable media, or any othersuitable local or remote memory component. Storage 213 may store anysuitable data, instructions, or information, including software andencoded logic, utilized by WD 210. Storage 213 may be used to store anycalculations made by processor 212 and/or any data received viainterface 211.

Interface 211 may be used in the wireless communication of signallingand/or data between WD 210 and network node 200. For example, interface211 may perform any formatting, coding, or translating that may beneeded to allow WD 210 to send and receive data from network node 200over a wireless connection. Interface 211 may also include a radiotransmitter and/or receiver that may be coupled to or a part of antenna211 a. The radio may receive digital data that is to be sent out tonetwork node 201 via a wireless connection. The radio may convert thedigital data into a radio signal having the appropriate channel andbandwidth parameters. The radio signal may then be transmitted viaantenna 211 a to network node 200.

Antenna 211 a may be any type of antenna capable of transmitting andreceiving data and/or signals wirelessly. In some embodiments, antenna211 a may comprise one or more omni-directional, sector or panelantennas operable to transmit/receive radio signals between 2 GHz and 66GHz. For simplicity, antenna 211 a may be considered a part of interface211 to the extent that a wireless signal is being used.

In some embodiments, the components described above may be used toimplement one or more functional modules used in a collision-blockingmethod for hash tree based time stamping. The functional modules maycomprise software, computer programs, sub-routines, libraries, sourcecode, or any other form of executable instructions that are run by, forexample, a processor. In general terms, each functional module may beimplemented in hardware and/or in software. Preferably, one or more orall functional modules may be implemented by processors 212 and/or 202,possibly in cooperation with storage 213 and/or 203. Processors 212and/or 202 and storage 213 and/or 203 may thus be arranged to allowprocessors 212 and/or 202 to fetch instructions from storage 213 and/or203 and execute the fetched instructions to allow the respectivefunctional module to perform any features or functions disclosed herein.The modules may further be configured to perform other functions orsteps not explicitly described herein but which would be within theknowledge of a person skilled in the art.

The methods according to the present invention is suitable forimplementation with aid of processing means, such as computers and/orprocessors, especially for the case where the processing element 202,212 demonstrated above comprises a processor handling securityfunctions. Therefore, there is provided computer programs, comprisinginstructions arranged to cause the processing means, processor, orcomputer to perform the steps of any of the methods according to any ofthe embodiments described above and those roughly summarized withreference to FIG. 12. The computer programs preferably comprises programcode which is stored on a computer readable medium 300, as illustratedin FIG. 14, which can be loaded and executed by a processing means,processor, or computer 302 to cause it to perform the methods,respectively, according to embodiments of the present invention,preferably as any of the embodiments described with reference to FIG.12. The computer 302 and computer program product 300 can be arranged toexecute the program code sequentially where actions of the any of themethods are performed stepwise. The processing means, processor, orcomputer 302 is preferably what normally is referred to as an embeddedsystem. Thus, the depicted computer readable medium 300 and computer 302in FIG. 14 should be construed to be for illustrative purposes only toprovide understanding of the principle, and not to be construed as anydirect illustration of the elements.

The invention claimed is:
 1. A method of verifying authenticity of apiece of data, the method comprising: deriving a plurality of one-timesigning keys of signer's one-time signing key hash chain by, for eachrespective one of the one-time signing keys, using a one-way functionthat directly operates on a same secret key of the signer and a functionof an index of the respective one-time signing key; providing a hashvalue for the piece of data by using a hash function that operates onparameters including the piece of data and one of the derived one-timesigning keys; using the hash value for the piece of data to obtain atime stamp for the piece of data; using the time stamp and the one ofthe derived one-time signing keys to form a signature for the piece ofdata; and using the signature to verify authenticity of the piece ofdata to another entity, wherein the index is an index in the hash chain,all values of the hash chain are bound by a root of a hash tree on topof a sequence formed by the one-time signing keys, and wherein a publickey of the signer includes the root.
 2. The method of claim 1, whereinthe function of the index is the index itself.
 3. The method of claim 1,wherein the one-way function is a cryptographic message authenticationcode function.
 4. The method of claim 1, wherein the one-way function isa hash function.
 5. The method of claim 1, comprising registering theprovided hash value.
 6. The method of claim 1, comprising providing aone-time proof of knowledge of the one-time signing key to a signingauthority entity without revealing the one-time signing key.
 7. Themethod of claim 6, wherein the one-time proof of knowledge includes ahash path for the hash value, and the providing of the one-time proof ofknowledge to the signing authority includes sending the index of theone-time signing key, the hash value and the hash path.
 8. The method ofclaim 1, comprising sending a signing request to a signing authority fora plurality of pieces of data, wherein each piece of data is assigned arespective index consecutively by using one-time signing keys withtime-forwarded one-time signing key indexes.
 9. The method of claim 1,comprising applying a time fraction hash tree splitting a time slotcorresponding to the index into time fractions such that the time slotis divided into fractions according to the number of leafs of the timefraction hash tree.
 10. An electronic device comprising a processingcircuitry arranged to verify authenticity of a piece of data, whereinthe processing circuitry is arranged to perform a method comprising:deriving a plurality of one-time signing keys of signer's one-timesigning key hash chain by, for each respective one of the one-timesigning keys, using a one-way function that directly operates on a samesecret key of the signer and a function of an index of the respectiveone-time signing key; providing a hash value for the piece of data byusing a hash function that operates on parameters including the piece ofdata and one of the derived one-time signing keys; using the hash valuefor the piece of data to obtain a time stamp for the piece of data;using the time stamp and the one of the derived one-time signing keys toform a signature for the piece of data; and using the signature toverify authenticity of the piece of data to another entity, wherein theindex is an index in the hash chain, all values of the hash chain arebound by a root of a hash tree on top of a sequence formed by theone-time signing keys, and wherein a public key of the signer includesthe root.
 11. The electronic device of claim 10, wherein the electronicdevice is a wireless device.
 12. The electronic device of claim 10,wherein the electronic device is a network node.
 13. A nontransitorycomputer readable storage medium comprising a computer programcomprising instructions which, when executed on a processor of anelectronic device, causes the electronic device to perform a method ofverifying authenticity of a piece of data, the method comprising:deriving a plurality of one-time signing keys of signer's one-timesigning key hash chain by, for each respective one of the one-timesigning keys, using a one-way function that directly operates on a samesecret key of the signer and a function of an index of the respectiveone-time signing key; providing a hash value for the piece of data byusing a hash function that operates on parameters including the piece ofdata and one of the derived one-time signing keys; using the hash valuefor the piece of data to obtain a time stamp for the piece of data;using the time stamp and the one of the derived one-time signing keys toform a signature for the piece of data; and using the signature toverify authenticity of the piece of data to another entity, wherein theindex is an index in the hash chain, all values of the hash chain arebound by a root of a hash tree on top of a sequence formed by theone-time signing keys, and wherein a public key of the signer includesthe root.